One of the biggest challenges athletes face when competing or training, particularly in moderate to hot temperature conditions, is heat. Not only must the athlete cope with heat from the external environment, but he/she also must cope with heat generated within his/her own body as a result of physical exertion.
Substantial heat may be generated in a person's body as a result of physical activity and exertion. In general, a body's core temperature rises with increased physical activity. Typically, less than about 25% of the energy created during physical activity is converted into work energy (e.g., energy used to move the body and/or resist an applied force). The remaining 75%+ of the created energy typically must be dissipated as released heat. The human body's most effective mechanism for dealing with excess heat is through evaporative cooling. When a person's core body temperature rises to a certain level, the body will start to sweat. When this liquid sweat evaporates, the physical conversion of the liquid to its corresponding gas form (i.e., the drying) draws heat from the nearest heat source. In the case of sweat, the nearest heat source is the skin. In this manner, sweating cools a person due to the evaporative cooling action as the sweat dries. This evaporation of sweat is dependent upon various factors, including, for example, the water vapor pressure (or relative humidity) of the air in contact with the skin. Air movement also is an important factor. For example, ambient air gains humidity as it picks up moisture during evaporation of sweat. In the absence of adequate air movement (ventilation), this humidified air becomes trapped in areas surrounding the skin, thus inhibiting the cooling potentially available through the continued evaporation of sweat.
Failure to properly release and move heat away from the body during exercise or physical exertion in a warm environment can cause a dangerous rise in a person's body temperature, potentially resulting in adverse health consequences, such as heat exhaustion or heat stroke.
Various known garment features are available and used to assist athletes in coping with excess heat generated as a result of physical exertion. For example, mesh venting has been used in garments to help dissipate heat. In sports apparel, it is common to see underarm vents provided by very small or closed-hole meshes, or by small eyelets provided through the fabric. While helpful, such meshes or vents typically are too small or too impermeable to provide adequate cooling effects.
Adequate cooling is not the only body temperature control issue that athletes and others face. The human body also may suffer adverse effects when exposed to cool or cold environmental conditions, particularly when exposed to such conditions for lengthy time periods. While people can simply add another layer of clothing to help stave off the adverse effects of a cold environment in some situations, the addition of clothing layers can adversely impact the wearer's ability to move, particularly when engaged in exercise, athletic events, or other activities requiring movement. The additional weight, bulk, and/or wind resistance resulting from the additional clothing also can adversely impact athletic performance. The adverse impacts on performance and comfort may deter some users from adequately dressing to protect themselves from the cold.